KR20090071343A - Control apparatus of the degree of superheat - Google Patents

Abstract

A controlling device of a degree of superheat is provided to increase the stability of control and to have the fast convergence of a measured value not only before the raising of the set value but also decreasing. A controlling device of a degree of superheat comprises: a target value filter(5) in which a set value of the degree of superheat is inputted; a target value change unit(3) giving the specific change about the set value of the degree of superheat in order to outputting a target value; a PID operation unit(1) outputting a control signal to an electric expansion valve according to the measured value and the target value outputted from the target value change unit; and a target value change control unit detecting the direction of the change of the set value of the degree of superheat. The target value change unit controls the change of the target value according to the change of the detected set value. The target value change control unit controls the target value change unit if the change of the target value when the set value decreases is more sluggish than when the set value increases.

Description

Control device of superheat degree {CONTROL APPARATUS OF THE DEGREE OF SUPERHEAT}

The present invention relates to a superheat degree control device in a refrigerating device.

Conventionally, the refrigeration apparatus which uses an electromagnetic expansion valve is known (patent document 1, patent document 2).

FIG. 7: is a figure which shows an example of the refrigeration apparatus which uses an electromagnetic expansion valve. FIG. The evaporator 21 installed in the freezer 20, the compressor and condenser in the freezer 22, the liquid feed solenoid valve 23, and the electromagnetic expansion valve 24 are annularly connected to the pipe to constitute a well-known refrigeration cycle. .

25 is an evaporator outlet temperature sensor which measures the temperature of the outlet side of the evaporator 21, 26 is an evaporator inlet temperature sensor which measures the temperature of the inlet side of the evaporator 21, 27 is a freezer which measures the temperature in the freezer 20 It is an internal temperature sensor, and the measurement signal by these sensors is input to the controller 28. As shown in FIG. The controller 28 has a control unit such as a microprocessor, a memory, a display unit, an operation unit and the like, and the evaporator outlet temperature measured by the evaporator outlet temperature sensor 25 and the evaporator inlet temperature sensor 26. The opening degree of the electromagnetic expansion valve 24 is controlled by PlD control according to the deviation between the measured value of the evaporator inlet temperature (superheat degree) and the measured value of the superheat degree and the set value (target value) of the superheat degree. The operation signal for controlling the output is output to the electromagnetic expansion valve 24. In addition, similarly to a normal refrigeration cycle, when the opening degree of the electromagnetic expansion valve 24 is operated in the containing direction, the superheat degree increases, and when the opening degree of the electromagnetic expansion valve 24 is operated in the opening direction, the superheat degree decreases.

Moreover, in PID control, the two degree of freedom PID control which can set the disturbance suppression characteristic and the target value following characteristic independently of each other is known (nonpatent literature 1).

Patent Document 1: Japanese Patent Publication No. 60-45779

Patent Document 2: Japanese Patent Application Laid-Open No. 06-259104

[Non-Patent Document 1] Kazuo Hiroy, `` Theory and Application of Control System Technology '', Published by Seonwon Electric Co., Ltd., September 10, 1992, p.40-43

Unlike a domestic air conditioner or the like, a refrigerating device used for work is used in combination with each of the elements shown in FIG. 7 according to the capability and the use (site demand) required at the installation site.

Some of the refrigeration apparatus does not lower the low-pressure pressure without increasing the superheat degree, and the temperature inside the freezer does not decrease, and on the contrary, the refrigerating device does not cool unless the superheat degree is lowered to the liquid back state. Thus, the optimum value of superheat degree differs with a refrigeration apparatus. Moreover, even if it is a refrigeration apparatus of the same structure, the optimum superheat degree may differ by conditions, such as an installation method and an installation place. Thus, the superheat set value is adjusted while raising or lowering during field adjustment, that is, during cool down during commissioning.

Since the control during the cool down is a control for maintaining the superheat degree constant while the heat energy in the freezer is decreasing, the closing frequency of the electromagnetic expansion valve 24 tends to have a high operation frequency. Therefore, undershoot is more likely to occur undershoot than overshoot.

In theory, there is no negative sign value in the superheat degree. In other words, the liquid back state below the superheat degree of 0 ° C. is not a change in the sensible heat that can be measured by the sensor, so that it is not controlled as a measured value and causes a delay in the control output, which causes deterioration of the control. .

8 is a diagram illustrating an example of a control response when the set value of the superheat degree is changed. In this figure, the vertical axis represents superheat degree and the horizontal axis represents time.

As shown in the figure, when the superheat degree setting value S0 is raised, an overshoot occurs in the measured superheat degree P0 (A in the drawing), and an undershoot occurs when it is lowered (B in the drawing).

Since the overshoot A when the set value S0 is raised is all sensible heat, the overshoot A is input to the PID operation unit of the controller 28 as a deviation, but the undershoot B when the overheat degree is set is lowered. Since the part (part of overheating below 0 degreeC) is not sensible heat, it is not input to a PID calculating part as a deviation, and causes a deterioration of control.

Therefore, in the superheat control of the solenoid expansion valve 24, when the overheat set value is raised or lowered, the allowable overshoot amount (undershoot amount when lowered) is different and the overheat set value is increased. The risk of worsening the control (undershoot) in the case of lowering the superheat setting value rather than overshooting is high.

For the above reasons, in the conventional control, it is necessary to perform the control output smoothly as a whole in accordance with the control characteristics in the case of lowering the set value of the superheat degree in consideration of the safety side.

9 is a diagram illustrating an example of a control response when the control parameter is set so that the undershoot is optimal when the superheat degree setting value is lowered.

When the parameter is set so that the measured value P0 of the superheat degree is quickly converged when the set value SO of the superheat degree is lowered (C in the drawing), the set value of the superheat degree ( When S0) is raised, the increase in the measured value P0 of the degree of superheat becomes slow, and the convergence becomes slow.

As described above, when the control characteristic in the case of lowering the set value of the superheat degree is adjusted, the control response when the set value is raised becomes more than necessary, and there is a problem that adjustment in the field is difficult.

In addition, according to the invention described in Patent Literature 1, since the gain can be changed in the case of -deviation and + deviation, it is preferable to control during the cooling down. However, since the deviation caused by the change in the measured value and the deviation caused by the change in the set value are treated in the same way, the problem remains when the control is performed while adjusting the set value.

The change in the measured value of superheat control (i.e., the superheat degree) is slow, but the change in the set value becomes a sudden step response. In the method of Patent Literature 1, the gains in the case of-deviation and + deviation are determined according to the deviation generated when the set value is changed for safety, and the operation when the measured value changes There is room for improvement in that it becomes gentle (not optimal).

It is also conceivable to use two degrees of freedom PID control for the purpose of improving the behavior (overshoot / undershoot) at the time of setting change.

Here, the two degrees of freedom PID control will be briefly described.

10 is an example of a functional block diagram of a general two degrees of freedom PID control. Here, 31 is a PID calculating unit, 32 is a control target, and 33 is a target value filter.

As shown in the figure, the control expression of the two degrees of freedom PID is configured by adding a target value filter 33 to a normal PID control equation (in this example, the measured value differential preceding type PID control equation of one degree of freedom).

Only the set value SV is input to the target value filter 33, and the measured value change is not fed back. That is, the control characteristic with respect to the measured value change is adjusted by each control constant of P, I, D in the PID calculating part 31, and the target value filter 33 does not affect it. Therefore, by adjusting the values of the coefficients α, β, and γ of the added target value filter 33, only the control characteristics at the time of changing the set value can be adjusted without changing the control characteristics for the disturbance or the measured value change. This control expression is called two degrees of freedom PID.

When the two degrees of freedom PID control is used, the target value filter 33 does not directly input the steep step response at the time of the setting change directly to the PID expression (PID operation unit 1), but instead enters the value gradually after the change. In addition, changes in measured values when changing settings can be alleviated. That is, the approaching side can be adjusted to the values of the coefficients of α, β, and γ in the target value filter 33. Since this can suppress undershoot when the set value is lowered, it is an effective means for the superheat control during the cool down.

However, by simply using two degrees of freedom PID control, the above-described undershooting is likely to occur, and the undershooting caused by lowering the set value has a high risk of deteriorating the control, that is, nonlinearity. Can't solve it. In short, by simply using two degrees of freedom PID control, it is necessary to set the target value filter 33 so that the change in the target value is smoothed in accordance with the control characteristics in the case of lowering the set value in consideration of the safety side. When the set value is raised, the control response becomes smoother than necessary, and the adjustment remains difficult.

FIG. 11 is an example of the figure for explaining this state, (a) is the case where the value of the coefficient of the target value filter 33 is selected so that it may become optimal when the setting value is raised, (b) is the case where the setting value is lowered The control response when the value of the coefficient of the target value filter 33 is selected so as to be optimal to

As shown in Fig. 11A, in the case where the values of the coefficients α, β, and γ of the target value filter 33 are selected to (α1, β1, γ1) so as to be optimal when the set value is raised, As shown in E, when the superheat degree set value S1 rises to the step shape, the waveform of the output F1 of the target value filter 33 does not become a step waveform but rises to a predetermined value and then gradually rises. The measured value P1 of the degree of superheat converges quickly. However, as indicated by F in the figure, when the set value S1 is lowered to the step shape, the output F1 of the target value filter 33 becomes a waveform which gradually decreases after reaching the predetermined value, but the degree of superheat The measured value P1 of becomes vibratory and slows convergence.

On the other hand, as shown in Fig. 11B, when the values of the coefficients α, β, and γ of the target value filter are selected as (α2, β2, γ2) so as to be optimal when the set value is lowered, G in the figure is shown. As shown in the figure, when the set value S2 is lowered to the step shape, the output F2 of the target value filter 33 is lowered by a smaller value than in the case of the above (a), and then becomes a waveform which descends gradually. The measured value of superheat (P2) quickly converges. However, as indicated by H in the figure, when the set value S2 rises in a step shape, the output F2 of the target value filter 33 rises by a smaller value than that in the case of (a), and then gradually rises. It becomes a waveform, and the measured value P2 of superheat degree rises slowly and convergence becomes slow.

Thus, even when two degrees of freedom PID control is used, it remains difficult to adjust in the same manner.

Then, an object of this invention is to provide the superheat degree control apparatus which can stabilize the behavior at the time of changing superheat degree set value.

Moreover, it is an object of the present invention to provide a superheat control device having a fast convergence of measured values and a high stability of control even after a change that raises the superheat set value is performed.

In order to achieve the above object, the superheat degree control device of the present invention is a control device for controlling the superheat degree by providing a control output to the electromagnetic expansion valve, and includes a target value filter into which a set value of the superheat degree is input, Target value changing means for giving a predetermined change to the set value of the superheat degree and outputting it as a target value, and PID for outputting a control signal to the electromagnetic expansion valve in accordance with the target value and the measured value output from the target value changing means. A target value change control means for detecting a direction of change of the set value of the superheat degree and controlling the degree of change of the target value output from the target value change means in accordance with the detected change direction of the set value of the superheat degree; To have.

The target value changing control means controls the target value changing means so that the change in the target value when the set value of the superheat degree decreases more smoothly than when the set value of the superheat degree rises. have.

The target value change control means selects the value of the coefficient of the target value filter in accordance with the direction of change of the set value of the superheat degree.

Further, the target value changing means has two target value filters having different transfer functions, and the target value changing control means is one of the two target value filters selected according to the direction of change of the set value of the superheat degree. The output of one of the target value filters is output to the PID operation unit.

The target value change control means outputs the set value of the superheat degree directly to the PID calculation unit without passing through the target value filter of the target value change means in accordance with the direction of change of the set value of the superheat degree. Whether or not the output of the target value filter is outputted to the PID calculation unit.

The target value change control means may set the value of the coefficient of the target value filter in the target value change means to be one degree of freedom PID control according to the direction of change of the set value of the superheat degree, Or, it is selected whether or not to set the value to be two degrees of freedom PID control.

In addition, the value of the coefficient in the said target value filter can be set arbitrarily.

According to such a superheat degree control apparatus of the present invention, as in the superheat degree control during the cool down, the control target or the allowable overshooting amount is quicker to change when the measured value falls toward the set value than when the measured value rises toward the set value. For the control target with a small amount of undershooting (high risk of deterioration of control over overshooting or undershooting), the control response in the case of raising the superheat set value can be optimized, and the control response in the case of lowering is also optimal. I can do it and can adjust it quickly.

In addition, the superheat degree set value can be adjusted smoothly, and the number of steps (the number of steps for field adjustment) matching with the refrigerating device can be reduced.

Furthermore, according to the present invention in which the value of the coefficient of the target value filter can be arbitrarily set, in addition to the above-described effects, it is possible to set more precisely in accordance with the refrigeration apparatus to be used and the intended use. Furthermore, it becomes possible to respond to a wide variety of refrigeration apparatuses and uses.

The superheat degree control apparatus of this invention is used for the same refrigeration apparatus as shown in the said FIG. 7, and is mounted in the controller 28 in the refrigeration apparatus shown in the said FIG.

1 is an example of the functional block diagram which shows the basic structure of the control apparatus of the superheat degree of this invention.

In this figure, 1 is a PID calculating unit, 2 is a control target, 3 is a target value changing unit having a target value filter 5, and 4 is a target value changing control unit controlling the target value changing unit 3.

The target value changing unit 3 has a target value filter 5 to which the set value SV of the superheat degree is input, and of the superheat degree changed by the transfer function H (s) of the target value filter 5. By outputting the set value as a target value to the PID operation unit 1, it is possible to control the mode of change of the target value.

The set value SV of the superheat degree is also input to the target value change control unit 4, and the target value change control unit 4 is a direction of the change of the set value SV of the superheat degree, that is, of the superheat degree. It detects whether the set value SV rises or falls and controls the mode of the change of the target value output from the target value changing unit 3 in accordance with the direction of the change.

 The PID control unit 1 performs a PID operation according to the deviation E between the target value and the measured value PV output from the target value changing unit 3, and supplies a control signal to the control target 2. .

Thus, the superheat degree control apparatus of this invention is equipped with the target value filter 5, and can perform PID control of 2 degrees of freedom. Further, the target value change control section 4 controls the target value change section 3 so that the change in the target value at the time of lowering becomes slower than the change in the target value when the superheat degree set value rises. As a result, undershooting when the set value of the superheat degree is lowered during the cooling down can be suppressed, and the measured value can be quickly converged even when the set value of the superheat degree is raised.

EMBODIMENT OF THE INVENTION Hereinafter, specific embodiment of the superheat degree control apparatus of this invention is described.

FIG. 2 is an example of a functional block diagram showing a configuration of a first embodiment of a control apparatus for overheating degree of the present invention.

In Fig. 2, 1 is a PID calculation unit, 2 is a control target, 5 is a target value filter, and 6 is a filter coefficient value selecting means. In this embodiment, the target value changing unit 3 is the target value filter 5 itself, and the target value changing control unit 4 is realized as the filter coefficient value selecting means 6.

The superheat degree set value SV as a target value is input to the target value filter 5 and the filter coefficient value selecting means 6. The target value filter 5 has a transfer function H (s) determined by the coefficients α, β, and γ, and multiplies the transfer function H (s) by the input superheat set value SV to multiply the PID calculation unit ( Output to 1). The PID operation unit 1 calculates the proportional term, the integral term and the derivative term based on the deviation E between the output from the target value filter 5 and the measured value PV of the superheat degree, and the electronic expansion as an operation stage. The control signal is output to the valve 24.

The filter coefficient value selecting means 6 detects whether the input superheat degree set value SV rises or falls, and when the set value rises, it is used for the calculation in the target value filter 5. As the value of the coefficient to be set, the optimum values (α1, β1, γ1) are set when the set value rises, and when the set values are lowered, the optimal values (α2, β2, γ2) are set when the set value decreases. Set it. For example, the change in the target value when the set value is lowered becomes slower than the change in the target value when the set value is raised.

3 is an example of a flowchart showing the flow of a process in the first embodiment of the superheat degree control device of the present invention. The superheat degree control apparatus of this invention repeats the process shown in this FIG. 3 for every predetermined control period.

When the process is started, first, the set value SV of the superheat degree is read, and it is determined whether or not the set value SVn of the present superheat degree is larger than the set value SVn · 1 in the previous control period. (Step S11). The set value SV of the superheat degree is set by operating the operation unit of the controller 28.

If the determination result of step S11 is YES, that is, the set value SVn of the superheat degree is higher than the previous set value SVn-1, the coefficients?,?,? Of the target value filter 5 When the set value is raised as a value, the values α1, β1, and γ1 which are optimal characteristics are set to be used (step S12). The target value filter 5 which uses the value of this coefficient is called a target rise filter. In this case, it becomes the characteristic shown to Fig.11 (a).

On the other hand, when the result of the determination in step S11 is no, it is determined whether or not the current set value SVn is smaller than the previous set value SVn-1 (step S13). If the result is an example, that is, the set value SVn of the superheat degree is lower than the previous set value SVn-1, it is set as the value of the coefficients α, β, and γ of the target value filter 5. When the value is decreased, the values α2, β2, and γ2 which are optimal characteristics are set to be used (step S14). The target value filter 5 using the value of this coefficient is called a target descent filter. In this case, it becomes the characteristic shown to FIG. 11 (b).

If the determination result of step S11 and step S13 is no (if there is no change in the set value SV), after executing step S12 or step S14, a target value filter is performed using the value of the set coefficient. The operation of (5) is executed (step S15), the PID operation is executed using the output (step S16), and an operation signal is output to the electromagnetic expansion valve 24 (step S17).

The above process is repeated for each predetermined control period.

FIG. 4 is a diagram illustrating an example of a control response in the first embodiment of such a superheat degree control device of the present invention.

When the superheat degree set value S3 rises (I in the figure), (α1, β1, γ1) is selected as the value of the coefficient of the target value filter 5, and thus the target value filter becomes a filter when the target value rises. The output F3 of (5) becomes a waveform which rises gradually after going up to a predetermined value, and the measured value P3 of superheat degree converges rapidly. In addition, when the superheat degree set value S3 falls (J in the figure), since (α2, β2, γ2) is selected as the value of the coefficient of the target value filter 5, the target value falls, so that the target The output F3 of the value filter 5 becomes a waveform gradually descending after falling down to a value smaller than the predetermined value, that is, a waveform slowly changing, and the measured value P3 of the superheat degree is quickly converged. . In this way, the change in the target value when the set value falls rather than the change in the target value when the set value rises, and the measured values converge quickly when both the set value rises and falls.

Thus, according to the superheat degree control apparatus of this invention, when the set value of superheat degree rises and falls, the value of the coefficient of the target value filter is selected as the optimal value in each case, Even after the change to raise the set value is performed, the convergence of the measured value is quick and the control with high stability can be realized even after the change to lower the set value.

5 is an example of a functional block diagram showing a configuration of a second embodiment of the superheat degree control device of the present invention. In this figure, the same components as those in Fig. 2 are denoted by the same reference numerals and description thereof will be omitted.

In FIG. 5, 51 is a filter at the time of the target value rising which has the value (alpha, alpha, beta, and gamma 1) of the coefficient which becomes an optimal characteristic when the superheat degree set value SV rises, 52 is the superheat degree set value SV. The target value falls filter having a value (α2, β2, γ2) which is an optimal characteristic when the target falls, 7 denotes an output of the filter 51 when the target value rises and the filter 52 when the target value falls Is a switching means for selecting an output of the input signal and inputting the same to the PID calculation section 1. Further, 8 inputs the superheat degree set value SV for each operation period of the manipulated variable, determines the change direction thereof, and outputs the filter 51 when the target value rises when the superheat degree set value SV rises. The switching means 7 is controlled so that the output of the filter 52 is input to the PID calculation section 1 when the target value falls when inputted to the PID calculation section 1 and the superheat degree set value SV drops. Filter selection means for outputting a control signal.

Thus, in this embodiment, the said target value change part 3 is the filter 51 at the time of the target value raise using the value ((alpha) 1, (beta) 1, (gamma) 1) of a coefficient, the value of the coefficient ((alpha) 2, beta 2, gamma 2). The filter selection means 8 corresponding to the target value change control part 4 is realized as the filter 52 and the switching means 7 at the time of the target value fall using the change of superheat degree set value SV. Direction is determined, and the output of the target value filter having the optimum characteristic is selected in the direction of the change so as to be supplied to the PID calculation unit 1.

Also with this embodiment, the same effect as the said 1st embodiment can be exhibited.

6 is an example of a functional block diagram showing a configuration of a third embodiment of the control device of the superheat degree of the present invention. In this figure, the same components as those in Fig. 2 are denoted by the same reference numerals and description thereof will be omitted.

In Fig. 6, 9 denotes an addition point for supplying the superheat set value SV to the input side of the target value filter 5 or for detecting a deviation between the target value and the measured value in the PID calculation unit 1. Switching means for switching whether to supply. In addition, 10 is a filter switching means which inputs the said superheat degree setting value SV for every operation cycle of an operation amount, determines the change direction, and controls the said switching means 9. When the superheat degree set value SV rises, the filter switching means 10 sets the switching means 9 so that the superheat degree set value SV does not pass through the target value filter 5. When the superheat degree set value SV drops, the superheat degree set value SV is switched to the target value filter 5 (two sides in the figure). Here, it is preferable that the value of the coefficient (alpha), (beta), (gamma) of the said target value filter 5 becomes the value ((alpha) 2, (beta) 2, (gamma) 2) of the coefficient of the filter at the time of falling of a target value.

Thus, when raising the superheat degree set value SV, the 1 degree of freedom PID control of the measured value differential preceding type is obtained, and the same control response as that of part A in FIG. 8 is obtained, and the superheat degree set value SV is obtained. When lowering, the same control response as that of J of FIG. 4 (G of FIG. 11) can be obtained.

In this way, control can be prevented from becoming unstable when the superheat degree is lowered.

In addition, as described in the above Non-Patent Document 1, the value of the coefficient derivative (1, 1, 0) of the target value filter 5 is set to (1, 1, 0), so that 1 of the measured value differential preceding type Freedom PID control.

Therefore, the value (α1, β1, γ1) of the coefficient of the target value filter 5 when the set value in the first embodiment is raised, or the target value rising filter 51 in the second embodiment. Α1 = 1, β1 = 1, and γ1 = 0 may be employed as the values (α1, β1, γ1) of the coefficient of the coefficient. At this time, as in the third embodiment, when the superheat degree set value is raised, one degree of freedom PID control of the measured value differential preceding type is obtained.

Further, the value of the coefficients α, β, and γ is not limited to (1, 1, 0), and other one degrees of freedom PIDs are set to (1, 1, 1) or (0, 1, 0), and the like. You may make it control.

In addition, in each embodiment mentioned above, although the values ((alpha) 1, (beta) 1, (gamma) 1), ((alpha) 2, (beta) 2, (gamma) 2) of the coefficient of the said target value filter 5 were made into fixed values, an operator May be arbitrarily set using an operation unit or the like of the controller 28. As a result, the ease of setting change can be finely optimized for each refrigeration device and each use, and the defensive range of the controller can be widened. For example, contrary to the above description, it is possible to cope with a control object to suppress overshoot when raising the set value, rather than undershoot when lowering the set value.

BRIEF DESCRIPTION OF THE DRAWINGS An example of the functional block diagram which shows the basic structure of the superheat degree control apparatus of this invention.

2 is an example of a functional block diagram showing a configuration of a first embodiment of a superheat degree control apparatus of the present invention.

3 is an example of a flowchart showing the flow of a process in the first embodiment of the control device of the superheat degree of the present invention.

4 is a diagram showing an example of a control response in the first embodiment of the control device of the superheat degree of the present invention.

5 is an example of a functional block diagram showing a configuration of a second embodiment of the superheat degree control device of the present invention.

6 is an example of a functional block diagram showing a configuration of a third embodiment of the superheat degree control device of the present invention.

7 shows an example of a refrigerating device using an electromagnetic expansion valve;

8 is a diagram illustrating an example of a control response when the superheat degree set value is changed.

9 is a diagram showing an example of a control response when the control parameter is set so that the undershoot is optimal when the superheat degree setting value is lowered.

10 is an example of a functional block diagram of a general two degrees of freedom PID control.

11 shows the case where the value of the coefficient of the target value filter 5 is selected to be optimal when the set value is raised, and the value of the coefficient of the target value filter 5 is selected to be optimal when the set value is decreased. A diagram illustrating an example of a control response.

** Description of the sign **

1: PID calculation unit, 2: control target, 3: target value changing unit, 4: target value changing controller, 5: target value filter, 6: filter coefficient value selecting means, 7: switching means, 8: filter selecting means, 9 : Switching means, 10: filter switching means, 20: freezer, 21: evaporator, 22: freezer, 23: liquid feed solenoid valve, 24: electronic expansion valve, 25: evaporator outlet temperature sensor, 26: evaporator inlet temperature sensor, 27: Temperature sensor in the freezer, 28: controller, 51: filter when the target value rises, 52: filter when the target value falls

Claims (7)

A control device for controlling the degree of superheat by providing a control output to an electromagnetic expansion valve, A target value filter having a target value filter into which a set value of the superheat degree is input, and giving a predetermined change to the set value of the superheat degree and outputting it as a target value; A PID calculator for outputting a control signal to the electromagnetic expansion valve in accordance with the target value and the measured value output from the target value changing means; And a target value change control means for detecting the direction of the change in the set value of the superheat degree and controlling the degree of change in the target value output from the target value change means in accordance with the detected direction of the change in the set value. Superheater control device characterized in that. The method of claim 1, The target value changing control means controls the target value changing means so that the change in the target value when the set value of the superheat degree decreases more smoothly than when the set value of the superheat degree rises. Control device of superheat. The method according to claim 1 or 2, And said target value change control means selects a value of a coefficient of said target value filter in accordance with a direction of change of a set value of said superheat degree. The method according to claim 1 or 2, The target value changing means has two target value filters having different transfer functions, The target value change control means outputs the output of any one of the two target value filters selected in accordance with the direction of change of the set value of the superheat degree to the PlD calculating section. controller. The method according to claim 1 or 2, The target value change control means outputs the set value of the superheat degree directly to the PID calculation unit without passing through the target value filter of the target value change means in the direction of the change of the set value of the superheat degree. Or select whether to output the output of the target value filter to the PID operation unit. The method according to claim 1 or 2, The target value change control means sets the value of the coefficient of the target value filter in the target value change means to a value to be 1 degree of freedom PID control in accordance with the direction of change of the set value of the superheat degree, or 2 degree of freedom PID control device characterized in that it is selected whether or not to be a value to be controlled. The method according to claim 1 or 2, The superheat degree control apparatus characterized by setting the value of the coefficient in the said target value filter arbitrarily.

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